Reference may be made to the following U.S. Pat. of interest Nos.: 3,184,963; 2,912,642; 2,849,669; 2,298,216; 2,275,532; 2,231,702; 2,183,078; 2,053,560.
Magnetostrictive material produces mechanical strains in response to a magnetic field produced by current in a coil surrounding the material. U.S. Pat. Nos. 2,912,642 and 3,184,963 disclose means for measuring the mechanical stresses in magnetostrictive material. In the disclosed systems, a mechanical force acting on the magnetostrictive material causes a distortion of the magnetic field. Means are provided for detecting the deformation of the magnetic field utilizing voltages induced in pickup coils so that the resulting detected pickup current is proportional to the applied mechanical force on the magnetostrictive material.
It is also known that varying the current in the coil surrounding the magnetostrictive material varies the induced strain and thereby causes very small changes in the dimensions of the magnetostrictive material. Accordingly, it has been proposed to calibrate the variation in coil input current versus the very small displacement of the magnetostrictive material so that such an arrangement could be used as a micro positioner. However, such a system has been found very difficult to calibrate due to a hysteresis effect, temperature variations, etc. For precision positioning devices using magnetostrictive material, i.e., micropositioning devices wherein the movement is in the range of 0.000001-0.010 inch (0.0000025-0.025 cm), the effects of hysteresis must be taken into consideration. Similarly, the effects of temperature variations on the amount of displacement of the magnetostrictive material in response to the input coil current must also be taken into account.
Accordingly, it is desired to provide apparatus and a method for measuring and/or controlling the motion of a magnetostrictive transducer so that such a transducer can be used as a micro-positioner device for use in applications requiring precise movement of components.